Sensor interposer employing castellated through-vias

ABSTRACT

An example sensor interposer employing castellated through-vias formed in a PCB includes a planar substrate defining a plurality of castellated through-vias; a first electrical contact formed on the planar substrate and electrically coupled to a first castellated through-via; a second electrical contact formed on the planar substrate and electrically coupled to a second castellated through-via, the second castellated through-via electrically isolated from the first castellated through-via; and a guard trace formed on the planar substrate, the guard trace having a first portion formed on a first surface of the planar substrate and electrically coupling a third castellated through-via to a fourth castellated through-via, the guard trace having a second portion formed on a second surface of the planar substrate and electrically coupling the third castellated through-via to the fourth castellated through-via, the guard trace formed between the first and second electrical contacts to provide electrical isolation between the first and second electrical contacts.

INCORPORATION BY REFERENCE TO RELATED APPLICATIONS

Any and all priority claims identified in the Application Data Sheet, or any correction thereto, are hereby incorporated by reference under 37 CFR 1.57. This application is a continuation of U.S. application Ser. No. 16/282,587, filed Feb. 22, 2019, which claims the benefit of U.S. Provisional Application No. 62/634,085, filed on Feb. 22, 2018. Each of the aforementioned applications is incorporated by reference herein in its entirety, and each is hereby expressly made a part of this specification.

FIELD

The present application generally relates to wearable biosensors, and more particularly relates to sensor interposers employing castellated through-vias.

BACKGROUND

Existing wearable biosensors, such as continuous glucose monitors, integrate an analyte sensor into the wearable device as a complete module assembly so that the device may be applied to the body and the sensor wire deployed into the body simultaneously with a single action. As a result, the sensor wire must be electrically connected and mechanically assembled to the device prior to deployment, during device manufacturing or assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more certain examples and, together with the description of the example, serve to explain the principles and implementations of the certain examples.

FIGS. 1 and 2 show example sensor interposers employing castellated through-vias formed in a printed circuit board (“PCB”);

FIGS. 3A-3B show an example sensor interposer employing castellated through-vias formed in a PCB;

FIG. 4 shows an example sensor interposer employing castellated through-vias formed in a PCB;

FIGS. 5A-5C shows an example wearable biosensor device including a sensor interposer employing castellated through-vias formed in a PCB; and

FIG. 6 shows an example method of manufacturing a sensor interposer employing castellated through-vias formed in a PCB.

DETAILED DESCRIPTION

Examples are described herein in the context of sensor interposers employing castellated through-vias. Those of ordinary skill in the art will realize that the following description is illustrative only and is not intended to be in any way limiting. Reference will now be made in detail to implementations of examples as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following description to refer to the same or like items.

In the interest of clarity, not all of the routine features of the examples described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another.

Some wearable biosensors employ one or more invasive sensor wires that are inserted into a wearer's skin. The sensor wire typically includes at least two discrete electrodes and has a quantity of a chemical substance, such as glucose oxidase (“GOX”), deposited on the end of the sensor wire that is inserted into the wearer's skin. The chemical then reacts with an analyte present in the wearer's interstitial fluid, which generates a current that can be sensed by the biosensor's electronics. However, because the amount of current generated can be very small, e.g., on the order of tens of nanoamps, and because these chemical substances can be sensitive to heat, the design and manufacture of the biosensor can be difficult. For example, the biosensor must be designed to prevent leakage currents that might interfere with the current generated by the reaction between the chemical substance and the analyte. In addition, manufacturing processes that include high-heat steps, such as soldering, may damage the chemical substance if it is heated.

To address these and other challenges, an example wearable biosensor may employ a main PCB having electronics, such as a microcontroller or wireless transceiver, a battery, etc. In addition, the example device employs a secondary PCB assembly to mechanically secure the sensor wire (generally referred to as an “interposer”), while also providing electrical contacts to different electrodes present on the sensor wire. The interposer can then be electrically and physically coupled to the main PCB, such as by soldering. To help reduce the amount of heat transferred to the interposer during soldering, an example interposer employs castellated through-vias to provide electrical connections between the main PCB and interposer and to provide soldering locations relatively thermally isolated from the sensor wire itself.

In this example, the interposer has through-vias formed around the perimeter of the interposer's footprint. The interposer is then cut from a larger PCB sheet such that the through-vias are cut, exposing the interior portions of the through-vias. The exposed interior portions of the through-vias may be aligned with corresponding electrical contacts on the main PCB and soldered together. Because the solder points are located inside of the through-vias and essentially at the other side of the PCB from the electronics on the interposer PCB, heat transfer from the soldering process to the interposer electronics, including the sensor wire, is substantially reduced. In addition, using through-vias enables one or more guard rings to be formed to encircle the interposer and provide electrical isolation between different electrical contacts formed on the interposer, such as the electrical contacts to different electrodes formed within the sensor wire.

This illustrative example is given to introduce the reader to the general subject matter discussed herein and the disclosure is not limited to this example. The following sections describe various additional non-limiting examples and examples of systems and methods for sensor interposers employing castellated through-vias formed in a PCBs.

Referring now to FIG. 1, FIG. 1 shows an example sensor interposer 100 employing castellated through-vias. In this example, the sensor interposer includes a planar substrate, a PCB in this example. Any suitable PCB material may be employed, including FR4, polyimide, etc. Two electrical contacts 112, 114 are formed on an upper surface of the PCB. Each electrical contact 112, 114 is sized and shaped to enable a sensor wire 120 to be electrically and physically coupled to it, e.g., by clamps, adhesive, or any other suitable physical coupling technique. In this example, the sensor wire is formed from two electrodes formed coaxially, and, prior to use, a sensor chemical (e.g., glucose oxidase) may be deposited on a distal end of the sensor wire, i.e. the end of the sensor wire to be inserted into the wearer's skin. The proximate end of the sensor wire exposes each electrode to enable each electrode to be electrically and physically coupled to a different one of the electrical contacts 112, 114. In this example, the working electrode (“WE”) is coupled to electrical contact 114, while the counter electrode (“CE”) is coupled to electrical contact 112. In addition, each electrical contact 112, 114 is electrically coupled to a castellated through-via formed on the perimeter edge of the PCB material. Once the interposer 100 is physically and electrically coupled to a main PCB, the castellated through-vias 118 will provide an electrical connection between the electrical contacts 112, 114 and sensor electronics positioned on the main PCB. While in this example, the interposer 100 has two electrical contacts 112, 114, some examples may employ multiple sensor wires, which may require additional electrical contacts based on the type(s) of sensor wire(s) employed. Further, in some examples, the sensor wire may include more than two electrodes. For example, multiple electrodes may be formed on top of each other in successive planar layers. Each layer may be coupled to a different electrical contact formed on the planar substrate. Further, different electrodes may have different sensor chemicals applied to them. Suitable sensor chemicals include chemicals to sense acetyl choline, amylase, bilirubin, cholesterol, chorionic gonadotropin, creatine kinase (e.g., CK-MB), creatine, DNA, fructosamine, glucose, glutamine, growth hormones, hormones, ketones, lactate, peroxide, prostate-specific antigen, prothrombin, RNA, thyroid stimulating hormone, or troponin.

In this example, the planar substrate 110 (or interposer substrate) also defines an opening 124 between the two electrical contacts. The opening provides physical separation between the two electrical contacts 112, 114, thereby providing some electrical isolation between them. In addition, the opening enables the formation of guard traces 116 a-b that do not intersect or contact the sensor wire 120. In some examples, the opening may be formed having a shape corresponding to one or more features formed on the main PCB to enable alignment. It should be appreciated, however, that such an opening is not required in all examples, and may be omitted based on design considerations.

In addition to the electrical contacts 112, 114, two guard traces 116 a-b have been formed on the interposer PCB. Each guard trace 116 a-b encircles a portion of the interposer PCB to provide electrical isolation between the two electrical contacts 112, 114. In this example, each guard ring includes a portion formed on the upper surface of the interposer PCB 110 that electrically couples two corresponding castellated through-vias. Each guard ring 116 a-b also includes a portion formed on the lower surface of the interposer PCB 110 that is also coupled to the same corresponding castellated through-vias to provide a closed loop of material encircling a portion of the interposer PCB. In combination with the opening, the two guard rings 116 a-b electrically isolate the two electrical contacts 112, 114 from each other. In some examples, one or both of the guard rings 116 a-b may be coupled to a ground plane to help dissipate leakage current.

In this example, the interposer 100 also includes a sensor wire 120 that is coupled to the two electrical contacts 112, 114. The sensor wire 120 in this example has two wire materials arranged coaxially, one of which operates as a working electrode and the other operates as a reference electrode or a counter electrode. To enable the two different coaxial portions of the sensor wire to couple to different electrical contacts, the interior wire material extends beyond the end of the exterior wire material, though a portion of it is covered by a polyurethane insulation 122. In this example, the interior wire material is physically and electrically coupled to one electrical contact 114 and the exterior wire material is physically and electrically coupled to the other electrical contact 112.

In this example, the sensor wire materials are (1) a platinum or platinum-coated wire, which is the interior wire material, and (2) a silver/silver-chloride (Ag/AgCl) material that is the exterior wire material. One end of the sensor wire 120 and a portion of the Ag/AgCl material are inserted into the patient's skin, while the other end of the sensor wire 120 is attached to the electrical contacts. The Ag/AgCl material is coupled to the first electrical contact 112, while the platinum material is coupled to the second electrical contact 114.

Referring now to FIG. 2, FIG. 2 illustrates another example sensor interposer 200 employing castellated through-vias. In this example, the interposer 200 is formed from a planar substrate, which is a PCB 210. Similar to the example shown in FIG. 1, the interposer 200 has two electrical contacts 230 a-b formed on it. A sensor wire 250 is physically and electrically coupled to the electrical contacts 230 a-b. In particular, the sensor wires has two coaxial electrodes 252 a-b, which are physically and electrically coupled to the respective electrical contacts 230 a-b. Each electrical contact 230 a-b is electrically coupled to a corresponding castellated through-via 220 b, 220 c by an electrical trace formed on the PCB 210. The castellated through-vias may later be physically and electrically coupled to electrical contacts on another PCB to allow electrical signals from the sensor wire 250 to be communicated to the other PCB.

The interposer 200 also includes a guard trace 240 formed on the PCB 210. The guard trace 240 traverses the PCB 210 between two castellated through-vias 220 a, 220 d and between the two electrical contacts 230 a-b, thereby electrically isolating them from each other. In this example, the guard trace 240 is formed both on the upper surface of the PCB (shown in FIG. 2) as well as on the lower surface, opposite the upper surface, where a further electrical trace is formed between the castellated through-vias 220 a, 220 d. However, in some examples, the guard trace 240 may only be formed on the same surface as the electrical contacts 230 a-b. In this example, unlike the example shown in FIG. 1, the PCB does not define a central opening. Thus, the guard trace 240 must run beneath the sensor wire 250 without contacting the sensor wire 250, which may disrupt electrical signals provided by the sensor wire 250 to the electrical contacts 230 a-b.

Referring now to FIGS. 3A-3B, FIG. 4A shows an example sensor interposer 300 employing castellated through-vias formed in a PCB. In this example, the interposer 300 has a PCB 310 planar substrate that defines a central opening 322. In addition, the PCB 310 has four castellated through-vias formed on its perimeter, while two castellated through-vias are formed on the perimeter of the central opening 322.

Two electrical contacts 312, 314 are formed on the upper surface of the PCB and are each electrically coupled to a corresponding castellated through-via formed on the perimeter of the central opening 322. The electrical contacts 312, 314 are arranged to physically and electrical couple to a sensor wire 220.

In addition to the electrical contacts 312, 314, two “wrap-around” guard traces 316 a-b are formed on the PCB 310. Each guard trace 316 a-b encircles a portion of the PCB 310 to provide electrical isolation between the two electrical contacts 312, 314. In this example, each guard trace 316 a-b includes a portion formed on the upper surface of the PCB 310 that electrically couples two corresponding castellated through-vias. Each guard trace 316 a-b also includes a portion formed on the lower surface of the PCB 310 that is also coupled to the same corresponding castellated through-vias to provide a closed loop of material encircling a portion of the PCB 310. In combination with the opening, the two guard traces 316 a-b electrically isolate the two electrical contacts 312, 314 from each other. In some examples, one or both of the guard traces 316 a-b may be coupled to a ground plane to help dissipate leakage current.

FIG. 3B shows a lower surface of the PCB 310. The view shown in FIG. 4B also illustrates the wrap-around guard traces 316 a-b, which are electrically coupled by a guard trace 316 c that couples the two castellated through-vias formed in the perimeter of the opening. In some examples, guard trace 316 c is not included, thus the two wrap-around guard traces 316 a-b are electrically isolated from each other on the PCB 310, though in some examples, they may be coupled to a common ground plane, such a common ground plane formed on a main PCB of a biosensor.

Referring now to FIG. 4, FIG. 4 shows an example sensor interposer 400 employing castellated through-vias formed in a PCB. Such an example sensor interposer 400 may be integrated within a wearable biosensor, such as a continuous glucose monitor (“CGM”). An example CGM may include a main PCB that includes various electronic components, including a processor, discrete electronic components, and a wireless transceiver. A battery may be mounted on and electrically coupled to the CGM's main PCB to supply power to the electronic components of the CGM.

The example sensor interposer 400 may be physically and electrically coupled to the main PCB to enable signals from the CGM's sensor wire, physically and electrically coupled to the sensor interposer 400, to be provided to electronic components on the main PCB, such as the processor.

The sensor interposer 400 in this example includes two electrical contacts 412, 414 formed on one side of the interposer 400, which are physically separated by an opening 422 defined in the perimeter of the interposer 400. Each electrical contact 412, 414 is electrically coupled to a castellated through-via. In addition, a guard trace 416 is formed on the same surface of the PCB 410 as the two electrical contacts 412, 414 and provides electrical isolation between the two electrical contacts 412, 414.

In addition to the electrical contacts and guard trace 416, the interposer 400 also includes additional electrical features. In this example, an electrical tracer designed as an antenna 430 is formed on the PCB 410, and electrically coupled to a castellated through-via to enable electrical and physical coupling to the CGM's main PCB. In some examples, still other electrical features may be provided on the PCB, including additional electrical contacts to physically and electrically couple one or more additional sensor wires.

In some examples, the interposer 400 may be formed separately from the main PCB, and the sensor wire may be physically and electrically coupled to the interposer 400 before the interposer 400 is physically and electrically coupled to the CGM's main PCB; however, as will be discussed with respect to FIG. 6, other sequences may be employed as well.

Referring now to FIGS. 5A-5C, FIG. 5A shows an example wearable biosensor device 500 that includes a sensor interposer 520 employing castellated through-vias. In this example, the wearable biosensor device 500 includes a main PCB 510 on which are positioned a sensor interposer 520 and a sensor controller 540. This example device 500 includes the example sensor interposer shown in FIG. 3; however, any suitable sensor interposer employing castellated through-vias may be employed.

In this example, the main PCB 510 also defines a surface feature 512, such as a pin that engages with an opening defined in the sensor interposer 520. FIG. 5B illustrates the main PCB 510, which has a surface feature 512 defined on it. The surface feature 512 provides an alignment feature to enable alignment of the sensor interposer 520 with the main PCB 510 and one or more electrical contacts formed on the main PCB 510. FIG. 5C illustrates a top-down view of the main PCB 510, which has the surface feature 512 formed and positioned to engage with a sensor interposer 520. In addition, the main PCB 510 has four electrical contacts 514 a-d formed to engage with the sensor interposer's castellated through-vias 522 a-d.

Referring now to FIG. 6, FIG. 6 shows an example method 600 for manufacturing a sensor interposer employing castellated through-vias formed in a PCB. The example method 600 will be described with respect to the example sensor interposer 100 shown in FIG. 1; however, example methods according to this disclosure may be employed to manufacture any suitable example sensor interposer according to this disclosure.

At block 610, a suitable planar substrate 110 is provided. In this example, the planar substrate 110 is a PCB formed of a suitable material, such as FR4 or polyimide. The planar substrate 110 in this example has a larger size than the designed sensor interposer 100. Thus, at a later step, the planar substrate 110 may be cut to the designed size for the sensor interposer 100.

At block 620, one or more through-vias 118 are formed in the planar substrate 110, such as in locations corresponding to a designed perimeter of a sensor interposer 100. Such through-vias 118 may be formed having substantially circular (or other) cross-sections, where a portion of the through-via's perimeter extends outside of the designed perimeter of the sensor interposer 100. In some examples, one or more through-vias 118 may be formed in an interior portion of the sensor interposer 100 as well. Such through-vias 118 may be formed around a designed perimeter of an opening to be defined in the sensor interposer 100. For example, referring again to FIG. 1, two through-vias were formed in the PCB 110 and were cut to form castellated through-vias when the central opening in the PCB 110 was formed. Any suitable number of through-vias may be formed according to different examples. In this example, four through-vias are formed on the designed perimeter of the sensor interposer, while two additional through-vias are formed on the designed perimeter of a central opening of the sensor interposer 100.

At block 630, the planar substrate 110 is cut along a designed perimeter of the sensor interposer 100, including cutting the through-vias to form castellated through-vias 118. In this example, the planar substrate 110 is further cut to form the central opening 124 and the castellated through-vias in the perimeter of the central opening 124.

At block 640, two electrical contacts 112, 114 are formed on the PCB 110 within the designed perimeter of the sensor interposer 100. In this example, the electrical contacts 112, 114 are formed to enable physical and electrical coupling of a sensor wire 120 and are formed on opposite sides of a designed central opening 124. In this example, both electrical contacts 112, 114 are formed on the same surface of the PCB 110; however, in some examples, they may be formed on opposite sides of the PCB 100. For example, if each electrode of a sensor wire is formed into a discrete wire, they may be coupled to opposite sides of the PCB 110. And while in this example, two electrical contacts are formed, in some examples, more than two electrical contacts may be formed. For example, if multiple sensor wires are to be affixed to the sensor interposer, a pair of electrical contacts may be formed for each sensor wire or sensor electrode.

In addition to forming the electrical contacts at block 640, an electrical trace from each electrical contact 112, 114 is formed to electrically couple the respective electrical contact 112, 114 to a corresponding castellated through-via. In some examples, the electrical traces may be serpentine to extend their length to reduce heat transfer from the castellated via to the electrical contact when the interposer is later soldered to the main PCB.

At block 650, one or more guard traces 116 a-b are formed on the PCB 110. In this example, electrical traces are formed to couple castellated through-vias to each other to electrically isolate the electrical contacts. For example, referring to FIG. 3A, electrical traces are formed between the castellated through-vias formed in the perimeter of the central opening 322 and a corresponding castellated through-via formed in the perimeter of the PCB 310. Such traces are formed on both the upper and lower surfaces of the PCB 310 to create guard traces that encircles the PCB 210. In addition, in this example, a guard trace 316 c is formed between the castellated though-vias formed in the perimeter of the central opening 322 to couple the two wrap-around guard traces 316 a-b; however guard trace 316 c is optional and may be omitted in some examples.

At block 660, a sensor wire 120 is coupled to the electrical contacts 112, 114. As discussed above, a sensor wire 120 may be a coaxial sensor wire 120 having two different wire materials with the inner wire material extending beyond the outer wire material at one end of the sensor wire 120. A portion of the exposed inner wire material may be physically and electrically coupled to one of the electrical contacts 114, such as by soldering or using a clip or other electrical coupling means. A portion of the outer wire material may be coupled to the other electrical contact 112 using any suitable electrical coupling means.

At block 670, suitable sensor chemistry, such as glucose oxidase, is deposited on the end of the sensor wire 120 distal from the sensor interposer 100.

At block 680, the sensor interposer 100 is coupled to a biosensor's main PCB. In this example, the sensor interposer 100 is soldered to the main PCB using each of the castellated through-vias formed in the perimeter of the sensor interposer. In some examples, the castellated through-vias formed in the perimeter of the central opening may be soldered instead or in addition.

While the steps of the method 600 above were described in a particular order, it should be appreciated that different orders may be employed according to different examples. For example block 630 maybe performed after block 650, or block 650 may be performed before block 640 or block 630.

The foregoing description of some examples has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Numerous modifications and adaptations thereof will be apparent to those skilled in the art without departing from the spirit and scope of the disclosure.

Reference herein to an example or implementation means that a particular feature, structure, operation, or other characteristic described in connection with the example may be included in at least one implementation of the disclosure. The disclosure is not restricted to the particular examples or implementations described as such. The appearance of the phrases “in one example,” “in an example,” “in one implementation,” or “in an implementation,” or variations of the same in various places in the specification does not necessarily refer to the same example or implementation. Any particular feature, structure, operation, or other characteristic described in this specification in relation to one example or implementation may be combined with other features, structures, operations, or other characteristics described in respect of any other example or implementation.

Use herein of the word “or” is intended to cover inclusive and exclusive OR conditions. In other words, A or B or C includes any or all of the following alternative combinations as appropriate for a particular usage: A alone; B alone; C alone; A and B only; A and C only; B and C only; and A and B and C. 

That which is claimed is:
 1. A sensor interposer comprising: a planar substrate defining a plurality of castellated through-vias; a first electrical contact formed on the planar substrate and electrically coupled to a first castellated through-via; a second electrical contact formed on the planar substrate and electrically coupled to a second castellated through-via, the second castellated through-via electrically isolated from the first castellated through-via; and a guard trace formed on the planar substrate, the guard trace electrically coupled between a third and a fourth through-via formed on the planar substrate, the guard trace isolating the first and second electrical contacts.
 2. The sensor interposer of claim 1, wherein the guard trace comprises a first portion formed on a first surface of the interposer substrate and electrically coupling a third castellated through-via to a fourth castellated through-via, and a second portion formed on a second surface of the interposer substrate and electrically coupling the third castellated through-via to the fourth castellated through-via, the guard trace formed between the first and second electrical contacts to provide electrical isolation between the first and second electrical contacts.
 3. The sensor interposer of claim 1, wherein the planar substrate defines an opening between the first and second electrical contacts, and wherein the third castellated through-via is formed in a perimeter of the planar substrate, and the fourth castellated through-via is formed in a perimeter of the opening, and wherein the guard trace is a first guard trace, and further comprising: a second guard trace formed on the planar substrate, the second guard trace having a first portion formed on the first surface of the planar substrate and electrically coupling a fifth castellated through-via to a sixth castellated through-via, the second guard trace having a second portion formed on the second surface of the planar substrate and electrically coupling the fifth castellated through-via to the sixth castellated through-via, the second guard trace formed between the first and second electrical contacts to provide electrical isolation between the first and second electrical contacts, and wherein the fifth castellated through-via is formed in a perimeter of the planar substrate, and the castellated sixth through-via is formed in a perimeter of the opening.
 4. The sensor interposer of claim 1, further comprising a sensor wire electrically coupled to the first and second electrical contacts.
 5. The sensor interposer of claim 4, wherein the sensor wire comprises a first wire material and a second wire material, the second wire material formed coaxially around the first wire material, a first portion of the first wire material extending beyond the second wire material at a first end of the sensor wire, wherein the first portion of the first wire material is electrically coupled to the first electrical contact, and the second wire materials is coupled to the second electrical contact.
 6. A method of forming a sensor interposer comprising: provide a planar substrate; forming a plurality of through-vias in the planar substrate; cutting a portion of the planar substrate to create an interposer substrate, the cutting comprising cutting through at least four of the through-vias to create at least four castellated through-vias; forming a first electrical contact on the interposer substrate and electrically coupling the first electrical contact to a first castellated through-via; forming a second electrical contact on the interposer substrate and electrically coupling the second electrical contact to a second castellated through-via, the second castellated through-via electrically isolated from the first castellated through-via; and forming a guard trace on the interposer substrate, the guard trace electrically coupled between a third and a fourth through-via formed on the planar substrate, the guard trace isolating the first and second electrical contacts.
 7. The method of claim 6, wherein the guard trace comprises: a first portion formed on a first surface of the interposer substrate and electrically coupling a third castellated through-via to a fourth castellated through-via, and a second portion formed on a second surface of the interposer substrate and electrically coupling the third castellated through-via to the fourth castellated through-via, the guard trace formed between the first and second electrical contacts to provide electrical isolation between the first and second electrical contacts.
 8. The method of claim 6, further comprising: defining an opening in the interposer substrate between the first and second electrical contacts, and wherein the third castellated through-via is formed in a perimeter of the planar substrate, and the fourth castellated through-via is formed in a perimeter of the opening, and wherein the guard trace is a first guard trace; and forming a second guard trace on the interposer substrate, the second guard trace having a first portion formed on the first surface of the interposer substrate and electrically coupling a fifth castellated through-via to a sixth castellated through-via, the second guard trace having a second portion formed on the second surface of the interposer substrate and electrically coupling the fifth castellated through-via to the sixth castellated through-via, the second guard trace formed between the first and second electrical contacts to provide electrical isolation between the first and second electrical contacts, wherein the fifth castellated through-via is formed in a perimeter of the planar substrate, and the castellated sixth through-via is formed in a perimeter of the opening.
 9. The method of claim 6, further comprising electrically coupling a sensor wire to the first and second electrical contacts.
 10. The method of claim 9, wherein the sensor wire comprises a first wire material and a second wire material, the second wire material formed coaxially around the first wire material, a first portion of the first wire material extending beyond the second wire material at a first end of the sensor wire, wherein electrically coupling the sensor wire comprises: electrically coupling the first portion of the first wire material to the first electrical contact, and electrically coupling the second wire materials to the second electrical contact.
 11. A wearable biosensor comprising: a sensor interposer comprising: a planar substrate; a first electrical contact formed on the planar substrate and electrically coupled to a first castellated through-via formed in the planar substrate; a second electrical contact formed on the planar substrate and electrically coupled to a second castellated through-via formed in the planar substrate, the second castellated through-via electrically isolated from the first castellated through-via; and a guard trace formed on the planar substrate, the guard trace electrically coupled between a third through-via and a fourth through-via, the third and further through-vias formed on the planar substrate, the guard trace isolating the first and second electrical contacts; a sensor wire physically coupled to the planar substrate, the sensor wire comprising at least two electrodes, a first electrode of the at least two electrodes electrically coupled to the first electrical contact, and a second electrode of the at least two electrodes electrically coupled to the second electrical contact; and a sensor chemical disposed on a distal end of the sensor wire; a printed circuit board (“PCB”) having a plurality of electrical contacts defined on a first surface of the PCB; and wherein the sensor interposer is physically coupled to the first surface of the PCB, and wherein the first, second, third, and fourth castellated through-vias are electrically and physically coupled to respective first, second, third, and fourth electrical contacts of the plurality of electrical contacts defined on the first surface of the PCB.
 12. The wearable biosensor of claim 12, further comprising a controller in communication with the sensor wire, the controller to receive sensor signals from the sensor wire, and determine an analyte concentration based on the sensor signals.
 13. The wearable biosensor of claim 12, wherein the guard trace comprises: a first portion formed on a first surface of the interposer substrate and electrically coupling the third castellated through-via to the fourth castellated through-via, and a second portion formed on a second surface of the interposer substrate and electrically coupling the third castellated through-via to the fourth castellated through-via, the guard trace formed between the first and second electrical contacts to provide electrical isolation between the first and second electrical contacts.
 14. The wearable biosensor of claim 12, wherein the planar substrate defines an opening between the first and second electrical contacts, and wherein the third castellated through-via is formed in a perimeter of the planar substrate, and the fourth castellated through-via is formed in a perimeter of the opening, and wherein the guard trace is a first guard trace, and further comprising: a second guard trace formed on the planar substrate, the second guard trace having a first portion formed on the first surface of the planar substrate and electrically coupling a fifth castellated through-via to a sixth castellated through-via, the second guard trace having a second portion formed on the second surface of the planar substrate and electrically coupling the fifth castellated through-via to the sixth castellated through-via, the second guard trace formed between the first and second electrical contacts to provide electrical isolation between the first and second electrical contacts, and wherein the fifth castellated through-via is formed in a perimeter of the planar substrate, and the castellated sixth through-via is formed in a perimeter of the opening.
 15. The wearable biosensor of claim 14, wherein the PCB defines a surface feature, the surface feature configured to engage with the opening defined in the sensor interposer planar substrate, the surface feature enabling alignment between the PCB and the sensor interposer.
 16. The wearable biosensor of claim 12, wherein the sensor chemical comprises glucose oxidase.
 17. The wearable biosensor of claim 12, wherein the sensor chemical comprises a chemical configured to react with one or more of glucose, lactate, or cholesterol.
 18. The wearable biosensor of claim 12, wherein the sensor wire comprises a first wire material and a second wire material, the second wire material formed coaxially around the first wire material, a first portion of the first wire material extending beyond the second wire material at a first end of the sensor wire, wherein the first portion of the first wire material is electrically coupled to the first electrical contact, and the second wire materials is coupled to the second electrical contact. 